In an electrically controlled throttle apparatus as shown in FIG. 16, a driving device such as a motor controls an opening degree of a throttle valve 102 in accordance with an accelerator position of an accelerator pedal stepped by a driver. In the throttle apparatus, a gap is formed between a bore inner periphery of a substantially tubular throttle body 101 and an outer circumferential periphery of a throttle valve 102, and the gap has a large influence of an airtightness of the throttle apparatus when the throttle valve 102 is in its full close position.
Conventionally, the throttle body 101 and the throttle valve 102 are independently manufactured in each different processes. Subsequently, a manufactured throttle valve 102 is combined with a manufactured throttle body 101 in accordance with an inner peripheral dimension of the manufactured throttle body 101 in a downstream process. Alternatively, a manufactured throttle body 101 is combined with a manufactured throttle valve 102 in accordance with an outer circumferential dimension of the throttle valve 102 in a downstream process. Thus, a predetermined gap is obtained between the bore inner periphery of the throttle body 101 and the outer circumferential periphery of a throttle valve 102. A throttle shaft 103 integrally rotates with the throttle valve 102. Both of the ends of the throttle shaft 103 are rotatably supported by cylindrical valve bearings 104 provided in the throttle body 101.
In molding methods according to JP-A-5-141540 and JP-B2-3315135, a manufacturing process of a throttle apparatus is reduced, and dimensional accuracy of a gap formed between a throttle valve and a throttle body is enhanced in a throttle apparatus of an engine. In the molding methods, the throttle body 101 and the throttle valve 102 shown in FIG. 17 are integrally molded of a resinous material in the same molding dies. At first the substantially tubular throttle body 101 is integrally molded of a resinous material. Subsequently, inner periphery (bore inner periphery) of the throttle body 101 is used as a molding die molding the throttle valve 102 when the throttle valve 102 is molded. Thus, a shape of an outer circumferential periphery of the throttle valve 102 is adapted to a shape of the bore inner periphery of the throttle body 101 in the above molding methods.
However, in the above molding methods of the throttle valve 102, the throttle body 101 is molded of a resinous material while the molded throttle body 101 is restricted by dies in its radial direction and in its substantially circumferential direction. Thus, the throttle valve 102 is molded of a resinous material while the throttle body 101 and the throttle valve 102 are restricted by the dies. The throttle body 101 and the throttle valve 102 are taken out of the dies, and gradually cooled. In this cooling period, the unrestricted throttle body 101 and the throttle valve 102 contracts. Namely, the throttle body 101 and the throttle valve 102 are deformed. Accordingly, the gap, which is formed between the bore inner periphery of the throttle body 101 and the outer circumferential periphery of the throttle valve 102, is deformed, and it is difficult to maintain the gap to be in a predetermined dimension.
To solve the above problem, according to an example 1 shown in FIG. 18, a throttle valve 1 is molded in a throttle body 5 as the throttle valve 1 is set to be in an opening position excluding its full close position. In FIG. 18, the rotation angle of the throttle valve 1 is set to be substantially perpendicular with respect to the full close position of the throttle valve 1. Thus, the outer circumferential periphery of the throttle valve 1 and the bore inner periphery 8 of a bore inner pipe 31 of a bore wall part 6 of a throttle body 5 are partitioned by dies. Here, a connecting part 105 connects the outer wall 6a of the bore wall part 6 of the throttle body 5 and the outer wall 7a of the motor housing part 7. In this structure, the outer circumferential periphery of the throttle valve 1 and the bore inner periphery 8 of a bore inner pipe 31 can be molded in the same dies in consideration of contraction (molding contraction, molding shrinkage) occurring in a molding process and deformation occurring in practical use. However, it is difficult to reduce dispersion of molding contraction. Here, dispersion of molding contraction occurring in the rotation axis (Y-axis direction) of the throttle valve 1 can be reduced by insert molding a throttle shaft (axial reinforce member, metallic shaft) 2 formed of a metallic material inside of a cylindrical part (resinous shaft part) 15 of the throttle valve 1. However, molding contraction occurring in a direction (radial direction, Z-axis direction) perpendicular to the rotation axis (Y-axis direction) of the throttle valve 1 cannot be reduced in its molding process. Accordingly, dispersion of a radial dimension of a disc part (resinous disc part) 14 of the throttle valve 1 increases due to contraction occurring in its molding process.